Treating high-strength nitrate wastewater by three biological processes

Three different types of bioreactors including an activated sludge reactor (ASR), a biologically mediated activated carbon fluidized bed reactor (BAFBR) and an upflow immobilized cell reactor (UICR) were studied. The results suggest that the carbon-nitrogen equivalent (CNE) ratio (in terms of COD/N) when using ASR to treat the wastewater will decrease as the sludge age increases while it will increase slightly as the influent concentration increases. The CNE ratios for BAFBR and UICR are 3.67 and 3.61 respectively. For the test between the two different growth types, the CNE ratio of suspended growth will be lower than the one of attached growth. The alkalinity-nitrogen equivalent (ANE) ratio (in term of Alk./N) for ASR is 3.78, for BAFBR it is 3.54, and for UICR it is 3.63. These ANE ratios are comparable with the theoretical value of 3.57. Under different operating conditions, slight changes of microorganisms are detected in Scanning Electron Microscope observation, but the dominant species, bacillus group, showed superior growth in all cases. Tests with the immobilized cells, biofilms will grow on the surface of them at the end of operation and the subsequent biochemical reactions will concentrate on the outer layer of biofilms. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.